1. Technical Field
This invention relates to a curable fluoropolyether composition which is curable at room temperature or under heat, has a low viscosity and high transparency, and exhibits improved water repellence, oil repellence, solvent resistance, chemical resistance and weather resistance.
2. Prior Art
Heretofore, curable fluoropolyether compositions have been used in a wide variety of applications owing to the properties of fluoroalkyl ether structure. For instance, JP-A 11-116685 discloses gel-like cured products of fluoropolyether having chemical resistance, solvent resistance and low moisture permeability. These gel-like cured products of fluoropolyether are utilized for the protection of semiconductor pressure sensors, electronic circuits and the like.
In general, curable fluoropolyether compositions are prepared by mixing a fluoropolyether compound as a base with a curing agent and a curing catalyst. It is desired that the curing agent and the curing catalyst be uniformly dissolved. For the curing agent in particular, choice must be made of the one which is highly soluble in the fluoropolyether compound because the curing agent is added in a larger amount than the hydrosilylation catalyst. If the curing agent is less soluble, the resulting composition becomes non-uniform and gives rise to undesirable phenomena including a remarkable increase of viscosity and phase separation during shelf storage.
It is known in the art that the solubility of the curing agent can be enhanced by incorporating a fluoroalkyl radical. One typical compound is of the following formula (2).
Herein and throughout the specification, Me is methyl.
This curing agent, however, has only three functional radicals per molecule. In general, the number of functional radicals on the crosslinking agent must be changed in order to adjust the hardness and physical properties (e.g., elongation) of cured products. Such a change is impossible with the above compound.
Also known is the curing agent having six functional radicals per molecule represented by the following formula (3).

This curing agent affords a cured product with a higher hardness than the aforementioned trifunctional curing agent. Regrettably, this curing agent is insufficiently soluble in the fluoropolyether base on account of a low fluorine content. The resulting composition becomes turbid and allows the respective components to separate during storage.